1. Field of the Invention
The present invention relates to a webbing retractor which is used by a seat belt device, and which, after a webbing is pulled out by a predetermined amount, can be constantly brought into a state in which a pullout operation of the webbing is prevented.
2. Description of the Related Art
A webbing retractor provided in a vehicle includes a built-in locking mechanism which, when necessary, prevents the rotation of a winding shaft in the direction in which the webbing is pulled out.
As the webbing retractor equipped with this type of locking mechanism, there are known a so-called emergency locking retractor (ELR) and a so-called automatic locking retractor (ALR): The ELR is constructed so that winding and pullout of the webbing is ordinarily allowed, and when sudden deceleration of a vehicle is detected by an acceleration sensor, the rotation of a winding shaft in the direction in which the webbing is pulled out is stopped instantaneously; the ALR is constructed so that, if the webbing is retracted slightly after having been pulled out to an arbitrary length, further pullout of the webbing is automatically prevented, and the pullout prevention state of the webbing is released by the webbing being substantially retracted to its full length, so that pullout of the webbing is allowed again.
A webbing retractor in which the ELR and ALR are used together has already been proposed by the assignee of the present application (as an example, see Japanese Utility Model Application Laid-Open (JP-U) No. 3-121059).
The webbing retractor disclosed in the above-described publication (JP-U No. 3-121059) comprises: a lock wheel which rotates in such a manner as to follow a winding shaft and which, when rotation of the lock wheel is prevented, operates locking means to prevent the winding shaft from rotating in the direction in which the webbing is pulled out; an ELR lever which is usually located at a position apart from the lock wheel and which, at a time when a vehicle suddenly decelerates, engages with the lock wheel so as to prevent rotation of the lock wheel; and an ALR lever which is selectively held at the position where the ALR lever engages with the lock wheel (i.e., engaged position) and at the position where the ALR lever is separated from the lock wheel (i.e., disengaged position). Further, a release gear for switching the position of the ALR lever is disposed coaxially with the winding shaft.
The release gear is provided to decelerate by the rotation of the winding shaft so as to rotate in the direction opposite to that of the rotation of the winding shaft, and when the webbing is brought into a state of being pulled out to its full length, the ALR lever is changed from the disengaged position to the engaged position, and when the webbing is brought into a state of being wound by its substantially full amount, the ALR lever is changed from the engaged position to the disengaged position.
On the other hand, the above-described webbing retractor, in which switching between the ELR and ALR is allowed as occasion demands, is not constructed so that the ELR is switched to the ALR in a state in which the webbing is completely pulled out to its full length, and in this webbing retractor, a structure is used in which switching from the ELR to the ALR is effected with somewhat sufficient time. Namely, the relationship of the engagement between the release gear and the ALR lever is set so that switching from the ELR to the ALR is effected in a state immediately before the webbing is pulled out to its full length (i.e., a state in which an end portion of the webbing having a length of 20 to 100 mm from a position where the webbing is engaged with the winding shaft is wound onto the winding shaft immediately before the state in which the webbing is pulled out to its full length). Accordingly, the usable length of the webbing becomes uneven and a usually unused portion of the webbing (the portion of the webbing from the switching position to the end of the webbing engaged with the winding shaft) remains as a dead turn portion on the winding shaft. For this reason, it is necessary to set the cut length of the webbing by taking account of the portion which remains as a dead turn portion, and therefore, the cut length of the webbing becomes longer, thereby resulting in an increase in cost.